Specialized drill bits are used to drill wellbores, boreholes, and other holes in the earth for a variety of purposes, including water wells, oil and gas wells, injection wells, geothermal wells, monitoring wells, holes used in mining, and the like. These drill bits come in two common types: roller cone drill bits and fixed cutter drill bits.
Well bores and other holes in the earth are typically drilled by attaching or connecting a drill bit to a means of rotating the drill bit. The drill bit can be attached directly to a shaft that is rotated by a motor, engine, drive, or other means of providing torque to rotate the drill bit. In oil and gas drilling, for example, the drill bit is typically connected to the lower end of a drill string that is in turn, connected at the upper end to a motor or drive at the surface, with the motor or drive rotating both the drill string and the drill bit together. The drill string typically comprises several elements that may include a special down-hole motor configured to provide additional or, if a surface motor or drive is not provided, the only means of turning the drill bit. Special logging and directional tools to measure various physical characteristics of the geological formation being drilled and to measure the location of the drill bit and drill string may be employed. Additional drill collars, heavy, thick-walled pipe, typically provide weight that pushes the drill bit into the formation. Finally, the drill pipe connects these elements (e.g. the drill bit, down-hole motor, logging tools, and drill collars, etc.) to the surface where a motor or drive mechanism rotates the entire drill string and, consequently, the drill bit, to engage the drill bit with the geological formation to drill the wellbore deeper.
As a wellbore is drilled, a fluid, typically a water or oil based fluid referred to as drilling mud, is pumped down the drill string through a bore of the drill pipe and any other elements present and through the drill bit. Other types of drilling fluids may be used, including air, nitrogen, foams, mists, and other combinations of gases, and for purposes of this application drilling fluid and/or drilling mud refers to any type of drilling fluid, including gases. In other words, drill bits typically have a fluid channel within the drill bit to allow the drilling mud to pass through the drill bit and out one or more jets, ports, or nozzles. The purpose of the drilling fluid is to cool and lubricate the drill bit, stabilize the wellbore from collapsing, to prevent any fluids present in the geological formation from entering the wellbore, and to carry the fragments and cuttings removed by the drill bit up an outer annulus between the drill string and the wellbore and out of the wellbore. While the drilling fluid is pumped through the inner bore of the drill string and out of the drill bit in a typical drill application, drilling fluid can be reverse-circulated. That is, the drilling fluid can be pumped down the outer annulus (e.g. the space between the exterior of the drill pipe and the wall of the wellbore) of the wellbore, across the face of the drill bit, and into the inner fluid channels of the drill bit through the jets or nozzles and up into the drill string.
Roller cone bits typically include at least two roller cones that have a plurality of cutting elements disposed on a surface of the roller cone. Legs extend from a forward end of the roller cone bit and secure the roller cones about their axes, leaving them free to rotate. In operation, as the drill bit is rotated, the roller cones contact a formation and the difference in angular velocity between the formation and the roller cone bit causes the roller cones to rotate about their axis. The cutters impact the formation as the roller cone rotates, crushing the formation. The cutters may be formed of a hardened material or have a coating of a hard material such as polycrystalline diamond.
Fixed cutter drill bits typically include a plurality of cutters, such as very durable polycrystalline diamond compact (PDC) cutters, tungsten carbide cutters, natural or synthetic diamond, or combinations thereof. These bits are referred to as fixed cutter bits because they employ cutting elements positioned on one or more fixed blades in selected locations or randomly distributed. Fixed cutter bits slide against the formation to remove the rock through a shearing operation. Through varying improvements, the durability of fixed cutter bits has improved sufficiently to make them cost effective in terms of time saved during the drilling process when compared to the higher up-front cost to manufacture the fixed cutter bits.
Recent advances in drilling and production technology include the drilling of one or more horizontal sections and/or offshoots that extend laterally away from a single vertical wellbore, to provide greater access to a laterally-disposed geologic formation of interest. The technology often includes the strategic placement of artificial plugs within the wellbore or an offshoot to temporarily isolate a particular section of the geologic formation adjacent the well for hydraulic fracturing, or “fracking”. Once the fracturing process is complete, these same plugs, which may typically be made from a combination of materials such as fiberglass, composite carbon fiber, steel, aluminum, cast iron and other materials that must be drilled out to allow the oil, gas or water to flow from the fractured formation back towards the primary wellbore. In a similar fashion, concrete “shoes” can also be placed in the well from time to time to seal off various portions of the wellbore, and which must later be drilled out or removed.
Typically, it is difficult to drill out or remove the artificial plugs and concrete shoes with the same type of drill bits that were used to drill the well in the first place. One reason is because the hard materials used in the artificial plugs are much more resistant and harder to drill efficiently when using a roller cone bit. Typical fixed-bladed drill bits with PDC cutters also may not cut the hard material effectively because these same hard materials can interact chemically with the PDC element bit to increase their susceptibility to brittle facture and premature wear, thereby rendering a PDC cutter-equipped drill bit less effective. Additionally, the hard material may be too hard for the PDC element to cut effectively and may damage the PDC elements.
A similar situation can arise, moreover, while drilling a borehole below the surface of an urban environment in order to create a utility passage, such as that used for water, sewer and natural gas piping, or conduit for electrical power and fiber optic cable networks. A drill bit used in urban applications could reasonably expect to encounter an underground formation comprising a mix of earth, concrete, steel and asphalt materials, etc., and which can be problematic for drill bits configured primarily for drilling rock.
Thus, there exists a need for a cost-effective and robust drill bit that can better drill through a variety of natural and/or man-made formations or objects, including earth, steel, aluminum, concrete, cast iron, and other hard materials.